A duplexer is a circuit that allows a transmitter and a receiver to share the same antenna to simultaneously transmit and receive signals at closely spaced frequencies. A duplexer usually comprises a first filter (i.e. the transmission filter) connected to a transmitter and a second filter (i.e. the reception filter) connected to a receiver. The passband of the transmission/reception filter is adjusted to let the transmission/reception signal pass through while blocking the propagation of the reception/transmission signal. Typically, an interconnection circuit physically connects both filters to the antenna.
The interconnection circuit usually comprises two transmission lines. The first transmission line physically connects both filters and the second transmission line connects the first transmission line to the antenna. Duplexers are commonly integrated into wireless communication terminals. However, the integration becomes problematic when the size of the duplexer is significant compared to that of the terminal.
Therefore, there is a need for an improved duplexer and an improved method of sharing an antenna between a receiver and a transmitter.